Arduino - Blinking LED


LEDs are small, powerful lights that are used in many different applications. To start, we will work on blinking an LED, the Hello World of microcontrollers. It is as simple as turning a light on and off. Establishing this important baseline will give you a solid foundation as we work towards experiments that are more complex.

Components Required

You will need the following components −

  • 1 × Breadboard
  • 1 × Arduino Uno R3
  • 1 × LED
  • 1 × 330Ω Resistor
  • 2 × Jumper


Follow the circuit diagram and hook up the components on the breadboard as shown in the image given below.


Note − To find out the polarity of an LED, look at it closely. The shorter of the two legs, towards the flat edge of the bulb indicates the negative terminal.


Components like resistors need to have their terminals bent into 90° angles in order to fit the breadboard sockets properly. You can also cut the terminals shorter.



Open the Arduino IDE software on your computer. Coding in the Arduino language will control your circuit. Open the new sketch File by clicking New.


Arduino Code

   Turns on an LED on for one second, then off for one second, repeatedly.

// the setup function runs once when you press reset or power the board

void setup() {  // initialize digital pin 13 as an output.
   pinMode(2, OUTPUT);

// the loop function runs over and over again forever

void loop() {
   digitalWrite(2, HIGH); // turn the LED on (HIGH is the voltage level)
   delay(1000); // wait for a second
   digitalWrite(2, LOW); // turn the LED off by making the voltage LOW
   delay(1000); // wait for a second

Code to Note

pinMode(2, OUTPUT) − Before you can use one of Arduino’s pins, you need to tell Arduino Uno R3 whether it is an INPUT or OUTPUT. We use a built-in “function” called pinMode() to do this.

digitalWrite(2, HIGH) − When you are using a pin as an OUTPUT, you can command it to be HIGH (output 5 volts), or LOW (output 0 volts).


You should see your LED turn on and off. If the required output is not seen, make sure you have assembled the circuit correctly, and verified and uploaded the code to your board.